Conventionally, pyroelectric elements have been known which are used as infrared detectors, such as human body sensors and fire sensors. A pyroelectric element includes a pyroelectric substrate and a pair of electrodes disposed on front and back sides of the pyroelectric substrate. The pyroelectric element is configured to have a light-receiving section composed of the pair of electrodes and a portion of the pyroelectric substrate interposed between the pair of electrodes. In the pyroelectric element, when the amount of infrared light applied to the light-receiving section changes, the polarization of the pyroelectric substrate is changed by a pyroelectric effect and electric charge is excited on the front and back sides of the light-receiving section. By extracting the electric charge from the pair of electrodes as a voltage, the pyroelectric element can function as an infrared detector. For example, PTL 1 describes a single-type pyroelectric element that includes a pyroelectric substrate having only one light-receiving section, a dual-type pyroelectric element that includes a pyroelectric substrate having two light-receiving sections, and a quad-type pyroelectric element that includes a pyroelectric substrate having four light-receiving sections. PTL 2 describes an infrared detector that includes a pyroelectric crystal and a silicon plate. The pyroelectric crystal has a light-receiving electrode on an upper surface thereof and a ground electrode on a lower surface thereof. The silicon plate is configured to support the pyroelectric crystal. The silicon plate is provided with a hole in a region opposite the light-receiving electrode. By having the hole in the silicon plate, the infrared detector can prevent an increase in thermal capacity and improve sensitivity for detecting infrared light.